The present disclosure generally relates to depth sensing, and specifically relates to estimation of absolute depth from polarization measurements.
Eye tracking is an important feature for head-mounted display (HMD) systems including systems used in artificial reality applications. An essential part of many features required to achieve compelling artificial reality relies on an accurate way to track optical axes of users' eyes. For example, a preferred solution to the vergence-accommodation problem is expected to rely critically on eye tracking so that a display can move to accommodate the expected depth of field that corresponds to the natural human vergence at any given time. Another example is foveated rendering, the technique that displays a variable resolution image on a display to match the variable spatial resolution capability of the human eye as the eye rotates to different positions around the display area. However, the problem is that human eyes rotate over a wide range of angles (e.g., up to 55 degrees) in all directions and can rotate very quickly and unpredictably, which limits capabilities of known techniques.
Conventional tracking systems that track features of the human eye often utilize a patterned illumination source (e.g., dots, lines) in conjunction with a standard imaging camera to determine a location of glints reflected off the eyes (i.e., the virtual image of the light source as observed behind the eye's surface). With enough glints detected, and a spherical assumption for the shape of the eyeball and cornea, an approximate eyeball geometry can be inferred. In this case, the optical axis is assumed to be perpendicular to the front center surface of the identified cornea. However, human eyes differ widely between people, often violating the spherical assumption and exhibit complicated sub-surface scattering events that can obscure sensitive measurement techniques that estimate the outer surface of the eye directly (e.g., using structured light, time-of-flight depth cameras, etc.).
Thus, the conventional tracking systems are typically limited by the quality of the optical path and do not provide sufficient accuracy needed for eye tracking in a HMD system.